Lower kafka_consumer highwater offset warning to debug (#23388)

* Lower highwater offset warning to debug in kafka_consumer

The warning fires routinely during leader failover, which is a
transient condition handled by the subsequent check run. Lowering
to debug avoids noisy agent logs.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

* Rename changelog fragment to match PR number

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: piochelepiotr

kafka_consumer/changelog.d/23388.fixed

@@ -0,0 +1 @@
+Lower log level from WARN to DEBUG for the message emitted when a consumer group has offsets for a partition but no stored highwater offset (typically during leader failover).

kafka_consumer/datadog_checks/kafka_consumer/kafka_consumer.py

@@ -325,7 +325,7 @@ def report_consumer_offsets_and_lag(
                     reported_contexts += 1
 
                     if (topic, partition) not in highwater_offsets:
-                        self.log.warning(
+                        self.log.debug(
                             "Consumer group: %s has offsets for topic: %s partition: %s, "
                             "but no stored highwater offset (likely the partition is in the middle of leader failover) "
                             "so cannot calculate consumer lag.",